The overall goal ofthe Epidemiology Project is to advance understanding of how reductions in malaria transmission mediated by sustained, intensified public health interventions that include universal deployment of long lasfing insecficide treated bed nets (LLINs) and artemisin combination treatment (ACT) alter the complex relationship between Plasmodium spp. parasites, malaria vectors and the human host in ways that can be translated to monitoring, evaluating and guiding regional and national malaria control programs. Major features of the project include i) three study sites that signify the breadth of P. falciparum and P. vivax endemicity and transmission potential in the SE Asia/Pacific region, ranging from holoendemic (north coast mainland Papua New Guinea [PNG]), meso/hyperendemic (East New Britain PNG), and hypoendemic (Western Province, Solomon Islands), ii) the execution of similar study designs in all three sites (longitudinal age-stratified childhood cohort studies and community surveillance for infection and morbidity), iii) the opportunity to compare directly the impact of interventions on control and elimination of P. falciparum versus P. vivax and, iv) close ties with national malaria control programs in the region. The specific aims are to; 1) Determine the effect of sustained control on patterns of Plasmodium spp infections and their contribution to malarial morbidity in children 1-5 years of age living in 3 areas with differing malaria endemicity 2) Assess effect of sustained control on force, complexity and dynamics of Plasmodium infections in children 6-12 years of age 3) Determine changes in the age-specific prevalence of infection and malaria-attributable illness 4) Study the gametocyte dynamics in P. falciparum and P. vivax infections 5) Monitor the changes in genetic diversity of Plasmodium spp. infections in the context of intensifying control activities Project 1 is central to the synergy of the ICEMR since Research Projects 2 (transmission) and 3 (Pathogenesis/immunity) will be done in the same endemic sites, with data shared and laboratory tests conducted by Core B (Database) and Core C (Molecular Diagnosfics).